The fuel supply apparatus of this type for the internal combustion engine to be mounted on the automotive vehicle, comprises a fuel pump for discharging fuel in a fuel tank, and a pressure regulator for adjusting supplying pressure (hereinafter simply referred to as “fuel pressure”) of the fuel to be supplied to an injector from the fuel pump. The pressure regulator generally comprises a case, a diaphragm provided in the case to separate the inner space of the case into two chambers, a pressure regulation valve provided on central portion of the diaphragm to be opened and closed in response to the fuel pressure varied in one of the two chambers, viz., a pressure regulation chamber and a back pressure chamber, and a spring (compression coil spring) provided in the case to urge the diaphragm against the fuel pressure varied in the pressure regulation chamber toward the back pressure chamber so that the pressure regulation valve can be maintained in a closed state to have the pressure of the pressure regulation chamber reach the preliminarily set pressure. In general, there are many cases in which the pressure regulator is arranged together with the fuel pump in the fuel tank.
The fuel supply apparatus equipped with the pressure regulator of this kind is known in the art, and comprises a back pressure raising circuit having an electromagnet valve and capable of introducing the fuel discharged from the fuel pump into the back pressure chamber so that the pressure (hereinafter simply referred to as “back pressure”) of the fuel in the back pressure chamber can be raised to change the pressure of the fuel to be regulated in the pressure regulation chamber into a higher pressure. The known fuel supply apparatus is designed to use another pressure regulator and a throttling element operable in cooperation with the pressure regulator other than the pressure regulator for adjusting the pressure of the fuel to be supplied to the injector so that the pressure of the fuel to be introduced into the back pressure chamber can be adjusted to a preliminarily set pressure (see for example Patent Document 1 listed below).
Another known fuel supply apparatus is provided with a three-way electromagnetic valve in a back pressure raising circuit to have fuel discharged from a fuel pump introduced into a back pressure chamber of a pressure regulator at the time of the three-way electromagnetic valve being energized, i.e., “ON” while to have the back pressure chamber opened to the inner pressure space of the fuel tank or to the atmospheric pressure space at the time of the three-way electromagnetic valve being deenergized, i.e., “OFF” (see for example Patent Document 2).
A further known fuel supply apparatus comprises a first feed pump, a second feed pump arranged in series at the downstream of the first feed pump, a first pressure regulator for adjusting the pressure of fuel discharged from the first feed pump to a first preliminarily set pressure, and a second pressure regulator having a back pressure chamber for introducing the discharge pressure therein at the time of the operation of the first feed pump to adjust the discharge pressure of the second feed pump to a second preliminarily set pressure, so that the fuel supply apparatus can supply the fuel at a relatively high pressure with the first feed pump and the second feed pump positioned at a relatively low head as well as can make it possible to perform the change between the high pressure and the low pressure (see for example Patent Document 3).
A still further known fuel supply apparatus comprises determination means for determining whether or not there can be vapors generated in pipes allowing fuel to pass therethrough, so that when the determination means determines that the vapors can possibly be generated in the pipes, the fuel under pressure is introduced into the back pressure chamber of the pressure regulator (see for example Patent Document 4).
A yet still further known fuel supply apparatus comprises a fuel supply pipe for connecting a fuel pump with an injector, a return pipe held in connection with the fuel supply pipe and having a plurality of throttling elements. From between the throttling pipes is taken out an intermediate pressure to be introduced into the back pressure chamber, while the fuel passing through the return pipe is returned to a fuel tank (see for example Patent Document 5).
A yet still further known fuel supply apparatus comprises a return pipe, and a valve for opening and closing the flow of the fuel to the return pipe (see for example Patent Document 6).
The other known fuel supply apparatus comprises a low pressure feed pump, a pressurization pump disposed in series at the downstream of the low pressure feed pump, a driving source for driving the low pressure feed pump and the pressurization pump with a common shaft, and a check valve provided between the pressurization feed pump and a common rail to have the fuel pass to the common rail from the pressurization feed pump through the check valve, a booster having a pressure chamber held in communication with the inside of the common rail and capable of pressurizing the fuel in the pressure chamber by a piston, and a motion converting mechanism capable of converting the rotation of the rotation shaft for driving the pump to the linear motion. The piston of the booster is driven through the motion converting mechanism at the starting time of the fuel supply apparatus, thereby making it possible for the pressure of the common rail to be rapidly increased at the starting time of the fuel supply apparatus (see for example Patent Document 7).
Further, the last known fuel supply apparatus is designed to estimate an evaporating fuel concentration in a fuel/air mixture in accordance with the value of compensation to compensate a fuel/air ratio to a target fuel/air ratio, and to drive a fuel pump at a rotation speed higher than a usual rotation speed when the evaporating fuel concentration exceeds a predetermined evaporating fuel concentration level (see for example Patent Document 8).